Field of the Invention
The invention relates generally to pneumatic post drivers
Description of Related Art
Posts must be driven into the earth for a wide variety of applications. One common post application is the erection or repair of fencing. Another common application is in the staking of trees and other guyed objects. Indeed, many other applications exist that call for the placement of posts of the various types including, but not limited to T Posts, Channel Posts, C Posts, Delineator Posts, Pipe, Sand Points, Ground Rods, Anchors, Z Posts, Large Tent Pegs, I Posts, W Posts, Concrete Form Pins, Beams, Round, Square or Rectangular Tubing, Wood Posts, Stakes, etc. For the sake of convenience, all post types will be generically referred to herein as simply posts or fence posts regardless of the end application.
Driving options typically include mallets and sledge hammers, a weighted tripod rig, manual post drivers of the type that include a tubular guide or sleeve that fits over the upper end of a post and is raised and then forcibly brought down upon the post to deliver repeated driving impacts, pneumatic post drivers, hydraulic post drivers, pile drivers, as well as a variety of make-shift tractor and power-tool techniques. Factors that influence a person toward one or more of these driving options include the number of posts needing to be driven, the relative heath and strength of the individual, the type of soil into which the post must be driven, the availability of a portable/extendable power supply, budget, site accessibility, and the like.
When a large number of posts need to be driven, or even a few number but the soil conditions are adverse, a power-driven device, such as a pneumatic or hydraulic unit may be indicated to drive the posts into the ground. Most power-driven devices of this type are large, heavy and expensive units often mounted on trucks, trailers or cranes for portability. These devices sometimes require multiple operators and considerable set-up time. They are often expensive and unwieldy.
Light duty powered devices for driving posts are disclosed in U.S. Pat. No. 6,667,242 to Cunningham, issued Aug. 17, 2004. The Cunningham patent discloses a post driver that includes a piston which rests at all times atop a post to be driven. The piston is housed within a weighted cylinder that is raised for each stroke pneumatically and falls by gravity with or without an optional spring or user assist. The entire disclosure of U.S. Pat. No. 6,667,242 is hereby incorporated by reference and relied upon. While the post driver disclosed in U.S. Pat. No. 6,667,242 is both effective and commercially successful, there remains a need for improved power post driving devices that are versatile in terms of the post sizes with which it can be used, that can be remotely operated from an elevated position atop of long post while the operator remains standing on the ground, and that does not incorporate complicated switching components susceptible to breakage or frequent maintenance.
Other examples of prior art post drivers may be observed in U.S. Pat. No. 348,870 to Trump issued Sep. 7, 1886, U.S. Pat. No. 3,838,741 to Pepe issued Oct. 1, 1974, and U.S. Pat. No. 4,429,751 Jackson issued Feb. 7, 1984. Trump (U.S. Pat. No. 348,870) discloses a valve-less, double-acting pneumatic hammer. The routing of air between top and bottom ends of the cylinder is determined entirely by position of the hammer piston. The hammer piston hits against an anvil that is spring-mounted in the bottom of the cylinder housing. Pepe (U.S. Pat. No. 3,838,741) also discloses a double-acting pneumatic hammer in one embodiment. Air is routed between top and bottom ends of the cylinder based entirely on the position of the hammer piston. There is no external air control valve. The hammer piston hits against an anvil that is supported by shock absorbing spacing shims. Jackson et al. (U.S. Pat. No. 4,429,751) discloses a single-acting pneumatic hammer system that uses an array of pneumatic, single-pilot air control valves directly responsive to hammer piston position. The Jackson air control valve system is highly complex, composed of several interacting single-pilot control valves arranged in various series and parallel circuits so that the hammer piston movement can be adjusted. A cushioning material is inserted between the hammer piston and the anvil.
Shortcomings in the post driver field, as typified in these prior art examples, are evident to the skilled artisan and include cumbersome and awkward designs that are generally unreliable, that consume large amounts of air pressure and that operate inefficiently to convert only a portion of the energy stored in the compressed air into downward driving force on a post thus requiring a long time and great quantities of compressed air to drive the post into the earth. The valve-less types of pneumatic drivers are grossly inefficient, whereas the prior art pneumatic drivers operated by external air control valves are woefully delicate for hard use in the field and difficult to repair.
Furthermore, prior art designs include anvils that are not well-suited to high cycle rates. High cycle rates can be especially useful when driving certain post types. It has been found that cycle rates on the order of 180-200 strokes per minute will generate a shock wave through the leading tip of the post to sonically loosen the soil as the post advances into the earth. Anvil designs of the prior art either frustrate operation at high cycle rates or are not constructed so as to withstand the rapid impacts over a reasonable service life.
There is therefore a need in the art for an improved pneumatic type post driver that is reliable, robust, which consumes very little air pressure, operates very efficiently to transfer a maximum amount of energy to a post, and that is capable of sustained use at high cycle rates.